(1) Field of the Invention
The present invention relates to an image forming device and an image forming method, and especially to a technology for preventing a positional shift of toner images of different colors that are transferred in layers onto an intermediate transfer member such as an intermediate transfer belt.
(2) Description of the Related Art
A 4-cycle color printer uses a technology of transferring toner images of yellow (Y), magenta (M), cyan (C), and black (K) in layers onto an intermediate transfer belt via one photoreceptor. In the 4-cycle color printer, in general, the toner images of different colors are formed on the photoreceptor at a timing based on a reference belt position of the intermediate transfer belt, and the formed toner images are transferred onto the intermediate transfer belt in layers. Therefore, the toner images of different colors have less incidence of the positional shift.
The reference belt position is recognized, for example, by detecting a hole provided in an intermediate transfer belt by a light transmission type sensor, or by detecting reflecting tape provided in an intermediate transfer belt by a reflection-type sensor. Also, U.S. Pat. No. 5,499,092 discloses an image forming device that forms a toner patch for detecting a reference belt position on an intermediate transfer belt so that a reflection-type sensor can detect the toner patch to recognize the reference belt position.
However, in order to provide a hole or reflecting tape in an intermediate transfer belt, a space for the hole or the reflecting tape needs to be secured in an area other than a toner image forming area and a contact area of a cleaner. This raises a need to increase the intermediate transfer belt in width and thus raises a need to increase the image forming device in size.
On the other hand, a toner patch can be formed in a toner image forming area and a contact area of a cleaner. This construction prevents an intermediate transfer belt from becoming wider and an image forming device from enlarging because there is no need to increase the intermediate transfer belt in width. However, running cost becomes higher because toner is consumed to form the toner patch.